Variable valve timing is utilized in vehicles with internal combustion engines to control the timing of engine cylinder valves in order to raise engine performance, increase fuel economy, increase drivability, and reduce emissions. Variable valve timing systems can be hydraulically controlled, an electronic controller of a powertrain control module directing high pressure oil to actuate oil pressure actuated cams for altering the valve timing.
The inventors herein have recognized various issues with the above system. In particular, powertrain control modules typically restrict cam movement at low oil pressure conditions, due to reduced cam controllability robustness. This restricted cam movement is disadvantageous under certain conditions, as it can render a vehicle unable to generate sufficient torque. For example, after towing a heavy load up a long incline, upon stopping a vehicle, an operator may be unable to launch a vehicle despite fully depressing the accelerator pedal due to the low engine speed and high oil temperature, which leads to low oil pressure. In this example, the powertrain control module restricts cam movement due to a low oil pressure inferred from the high oil temperature, and the engine speed is restricted by the torque converter, which stalls at a low engine speed. Consequently, the vehicle is immobilized because sufficient torque is not generated to launch the vehicle. In other examples, insufficient torque to launch a vehicle may occur under driving conditions including one or more of high altitude, ascending an incline, and towing a trailer, when at near-zero vehicle speed.
One approach that at least partially addresses the above issues is a method, comprising in response to a first condition comprising an oil pressure below a threshold oil pressure and an engine speed below a threshold engine speed, restricting cam movement while the vehicle is moving, and during a vehicle stopped condition, overriding the restricted cam movement. In another embodiment, a method comprises during a first vehicle moving condition, adjusting cam timing responsive to a requested torque and a requested vehicle speed, but irrespective of an available torque, and limiting cam timing adjustment responsive to oil over-temperature at increased loads. Furthermore, during a second condition following the first condition, the method comprises overriding the cam timing adjustment limits in response to the available torque being insufficient to meet the requested torque. In this way, it is possible to achieve the technical result of repositioning the cams via a variable valve timing system to increase available torque, even during a condition, when an oil pressure or an inferred oil pressure based on oil temperature may be low. In particular, in response to vehicle conditions, the method can supersede conventional cam repositioning control strategies based on inferred or actual oil pressure, in order to increase available torque.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.